384 SPECIAL HISTOLOGY. 



parts of bones, and those of the cranium ; in the latter, how- 

 ever, openings made by the trephine are in many cases filled 

 up, instead of fibrous membrane, with isolated patches of bone, 

 or even with an entire piece of bone; in fact, trephined 

 portions of bone have united exactly in the same way as has 

 been observed to take place with portions of bone half cut off 

 (Pauli). Hypertrophy of bone assumes the most various 

 forms, all of which may be reduced under two principal types: 

 1. deposits on the surface, or external hyperostoses, which are 

 formed chiefly from the periosteum; aud 2. internal or scleroses, 

 which consist in the filling up of the medullary cavities and 

 Haversian canals with new bone, and these two forms may 

 occur either separately or combined. The former takes place in 

 inflammations of the periosteum, either idiopathic or in con- 

 nection with cancer, arthritis, syphilis, &c, the latter not only 

 consecutively in old age, but also in rachitis, osteomalacia and 

 syphilis. With respect to the microscopic conditions of these 

 growths, Virchow deserves the credit of having distinctly 

 indicated (' Archiv, f. pathol. Anat. 1/ p. 135), that the bony 

 growths or osteophytes on the cranium are formed by a direct 

 ossification of connective tissue without any preliminary deve- 

 lopment of cartilage, which is also undoubtedly the case in the 

 filling up of the losses of substance in the cranium, in rege- 

 neration proceeding from the periosteum, and in most cases of 

 sclerosis. The newly formed osseous substance is sometimes 

 like the normal (many exostoses), sometimes more dense, with 

 small vascular spaces and large irregular lacuna?. Atrophy of 

 the bones is shown in their disappearance in totality in 

 consequence of chronic diseases, paralysis, anchylosis; or in 

 rarefaction of the osseous tissue analogous to senile atrophy, in 

 syphilis, lepra, mercurial cachexy, paralysis, &c. Death of 

 bone (necrosis) is observed in cases where the periosteum has 

 been destroyed ; in inflammations of that membrane and of the 

 bone, &c, for the most part attended with an excessive growth 

 of the remaining sound parts. Peculiar morbid conditions 

 exist in osteomalacia and rachitis, but in neither of these 

 diseases have microscopical researches afforded anything worth 

 mention here, except what has been made known by H. Meyer 

 and myself (11. cc.) with respect to ossification in rachitis. In 

 this case I have found: 1. that in the disproportionately large 



